The effects of commonly prescribed psychotropic drugs such as methylphenidate and dextroamphetamine on the behavior and learning of children from about 5 to 12 who show hyperactivity, impulsivity, and are categorized as having minimal brain dysfunction with consequent learning disabilities will be systematically studied with emphasis on research methodology. The effect of psychotropic drugs such as thioridazine and chlorpromazine on the learning and social behavior of institutionalized mentally retarded patients will also be studied. A number of dependent measures will be used to assess drug effects: teacher, parent, and physician ratings; psychological testing; a variety of experimental psychological tasks including learning, short-term memory, attention, and motor performance including steadiness and finger-mazes. Dose-response effects on all these measures will be carefully measured. Physiological effects of stimulant medication, both short- and long-term, will be evaluated. These will include cardiovascular effects such as heart rate, oxygen consumption, and blood pressure at rest and under exercise stress. The effects of these medications on growth and development will be measured in detail. Plans have been made to use the outstanding facilities in mass spectrometry of the University of Illinois, Chemistry Department to measure methylphenidate in blood and urine. Long term follow-up of children with minimal brain dysfunction, including those who are not being medicated as well as those who are will be given high priority, and these children will be compared to a carefully selected normal cohort group.